Move ScrollbarManager from core to platform and use as Scrollbar parent

third_party/WebKit/Source/platform/scroll/ScrollbarManager.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef ScrollbarManager_h
 #define ScrollbarManager_h
 
-#include "core/CoreExport.h"
-#include "platform/scroll/ScrollableArea.h"
+#include "platform/PlatformExport.h"
+#include "platform/heap/Handle.h"
+#include "platform/scroll/ScrollTypes.h"
+#include "platform/scroll/Scrollbar.h"
 
 namespace blink {
 
-class CORE_EXPORT ScrollbarManager {
+class PLATFORM_EXPORT ScrollbarManager
+    : public GarbageCollectedFinalized<ScrollbarManager> {
   DISALLOW_NEW();
 
   // Helper class to manage the life cycle of Scrollbar objects.
  public:
-  ScrollbarManager(ScrollableArea&);
+  ScrollbarManager();
+  virtual ~ScrollbarManager();
 
   void Dispose();
 
   Scrollbar* HorizontalScrollbar() const {
-    return h_bar_is_attached_ ? h_bar_.Get() : nullptr;
+    return h_bar_is_attached_ ? h_bar_ : nullptr;
   }
   Scrollbar* VerticalScrollbar() const {
-    return v_bar_is_attached_ ? v_bar_.Get() : nullptr;
+    return v_bar_is_attached_ ? v_bar_ : nullptr;
   }
   bool HasHorizontalScrollbar() const { return HorizontalScrollbar(); }
   bool HasVerticalScrollbar() const { return VerticalScrollbar(); }
 
   // These functions are used to create/destroy scrollbars.
   virtual void SetHasHorizontalScrollbar(bool has_scrollbar) = 0;
   virtual void SetHasVerticalScrollbar(bool has_scrollbar) = 0;
 
   DECLARE_VIRTUAL_TRACE();
 
  protected:
-  // TODO(ymalik): This can be made non-virtual since there's a lot of
-  // common code in subclasses.
   virtual Scrollbar* CreateScrollbar(ScrollbarOrientation) = 0;
   virtual void DestroyScrollbar(ScrollbarOrientation) = 0;
 
  protected:
-  Member<ScrollableArea> scrollable_area_;
-
   // The scrollbars associated with m_scrollableArea. Both can nullptr.
   Member<Scrollbar> h_bar_;
   Member<Scrollbar> v_bar_;
 
-  unsigned h_bar_is_attached_ : 1;
-  unsigned v_bar_is_attached_ : 1;
+  bool h_bar_is_attached_;
+  bool v_bar_is_attached_;
 };
 
 }  // namespace blink
 
 #endif  // ScrollbarManager_h